Circuit interrupter with damper body to reduce speed of moving terminal

ABSTRACT

After initial arc drawing movement the rodlike terminal of high voltage alternating current power fuse driven by a spring and gas pressure has its speed reduced by encountering a damper body which is normally latched in a stationary position until it is unlatched on impact by the terminal. Some of the kinetic energy of the moving terminal is dissipated by deforming metallic coupling parts and additional kinetic energy is absorbed in accelerating the damper body. A cross slide latch and a latch lever are employed to hold the damper body stationary in a fuse housing for release on impact by the terminal.

United States Patent CIRCUIT INTERRUPTER WITH DAMPER BODY TO REDUCE SPEED OF MOVING TERMINAL 15 Claims, 13 Drawing Figs.

U.S.Cl 337/275 lnt.Cl ..H0lh 85/02,

HOlh 85/36, HOIh 85/42 Field oiSearch 337/168,

References Cited UNITED STATES PATENTS 3,267,235 8/1966 Barta 2,247,704 7/1941 Triplett 2,087,744 7/1937 Triplett ABSTRACT: After initial are drawing movement the rodlike terminal of high voltage alternating current power fuse driven by a spring and gas pressure has its speed reduced by encountering a damper body which is normally latched in a stationary position until it is unlatched on impact by the terminal. Some of the kinetic energy of the moving terminal is dissipated by deforming metallic coupling parts and additional kinetic energy is absorbed in accelerating the damper body. A cross slide latch and a latch lever are employed to hold the damper body stationary in a fuse housing for release on impact by the terminal.

PATENTED DECZI l9?! SHEET 1 [IF 6 PATENTED DEEZI nan 3629.767

SHEET 5 OF 6 CIRCUIT INTERRUPTER WITII DAMPER BODY TO REDUCE SPEED OF MOVING TERMINAL This invention relates, generally, to high-voltage alternating-current power fuses and it has particular relationto such fuses of the dropout type disclosed in Barta U.S. Pat. No. 3,267,235, issued Aug. l6, 1966, although it is no limited to use in this particular fuse construction or in a dropout fuse.

In high-voltage power fuses for alternating-current system protection, the current to be interrupted produces an are on severance of the fusible element. One end of the arc terminates on a stationary terminal at the exhaust end of the fuse. The other end of the arc terminates on a tip of a rodlike terminal which is subsequently withdrawn into a constricted bore formed in material or materials that evolve large quantities of gas under the intense are heat. The amount of gas evolved in a function of bore materials, bore diameter, current magnitude and length of bore material exposed to the arc. As the gas is evolved, it is important that it be effectively vented, preferably at only the exhaust end of the fuse, so that the gas not only moves at high velocity as it exhausts but sweeps along the arc path in a single direction which causes constricting and cooling of the arc.

As the arcing period continues and the arc is lengthened by the withdrawing rodlike terminal, current zeros or arc zeros arrive at periodic times. These times, measured from the start of arcing, depend upon circuit frequency, fault initiating angle (relative to driving voltage zero), circuit power factor and current asymmetry decrement. At each current zero, there is an attempt made by the fuse to clear-this clearing being accomplished if the just-previous arc path can withstand the recovery voltage impressed across it. The ability to withstand this recovery voltage depends upon (a) the amount of gas generated by the are, (b) the arc length just prior to the cur rent zero, (c) the added terminal separation in the submillisecond and millisecond range after current zero is reached, (d) temperature of the arc terminals, (e) the amount of metallic vapor in the bore and the exhaust gases, and (f) the effectiveness of gas flow out of the exhaust. Point (a) in turn depends upon the fault current level, bore diameter and also arc length.

For a fuse of given voltage rating, the magnitude and natural frequency of the recovery voltage are not readily controllable by the fuse designed. Fault current levels in the full range from a minimum melt up to the interrupting rating of the fuse must be coped with. To handle the lower current ranges requires that certain bore sizes, within narrow limits, be assigned to specific ranges of element steps. Use of stationary terminal and rodlike terminal materials does not allow for much control over the amount of metallic vapors produced, these being controlled mostly by fault level and arcing time. Venting effectiveness is within the designer's control only to the point of achieving smooth flow up to the acoustic velocity at exit. Longer arc lengths make this control more difficult to maintain.

As can now be seen, a parameter of important significance that the fuse designer should seek to control is that of arc length. It has been found by extensive testing that, for a given fuse voltage size, a certain minimum gap or arc length (terminal separation) is required to clear. This circuit gap must be accompanied by sufficiently large gas generation. As gas volume is reduced (lower currents), longer minimum gaps are required. Difficulties arise when, at an early current zero, there is either insufficient gas generation of insufficient gap, and the fuse must await the next current zero. During this waiting period, the combination of current and long arc length produced by an ever more rapidly moving rodlike terminal, can generate so much gas so deeply within the fuse that even efficient venting at the exhaust end cannot prevent the buildup of excessive pressure within the fuse housing. Violent rupture of the fuse housing may result. These conditions, i.e., ofa justmissed current zero followed by an intolerably long are gap before next current zero, occur with many combinations of current level, current asymmetry and element size.

On may adjust the parameters of a fuse so that a specific combination of current-asymmetry and element size results in a safeclearin'g condition, only to find that a new combination (that gave safe clearing with previous design parameters) yields unsafe clearing conditions. However, what is needed is a method of controlling arc length beyond the minimum clearing gap. The rodlike terminal travel in the early stages should not be retarded, so that early clearings can take place. But, to cope with the situations where an early current zero is just missed, the rodlike terminal should be retarded in its later stroke so that arc length and subsequent gas generation are kept small enough to be contained until the next zero occurs. For-this purpose a mass pick up arrangement is employed in accordance with this invention. This technique is used because it offers the benefits of (a) highly predictable effects, (b) virtually unlimited range of effect and ease of study to select optimum parameters, and (0) action unaffected by environmental conditions of temperature and humidity. It also has a two-fold control effect-one immediate and one acting throughout the balance of stroke.

The action takes place as follows: At some selected point in the stroke of the rodlike terminal, it impacts on and couples to a stationary but floating damper body. Coupling involves essentially an inelastic impact. A predictable amount of rodlike terminal kinetic energy is lost in the impact which depends upon the relative masses of the rodlike terminal and the damper body. Further, velocity of the combination rodlike terminal damper body assembly immediately after impact is known, again being dependent upon their relative masses. For example, after inelastic impact of a l-pound rodlike terminal into a %-pound damper body, one-half of the terminal kinetic energy is lost as coupling deformation, and the combination assembly has an initial velocity of one-half the velocity of the rodlike terminal before impact. For a /&-pound rodlike terminal into a 2pound damper body, four-fifths of the terminal kinetic energy is lost and the combination assembly has an initial velocity of one-fifth of the velocity of the rodlike terminal before impact.

The technique used to obtain inelastic coupling of the damper body to the rodlike terminal at the selected pickup position is by a tapered pin jamming into a tapered hole. The tapered pin is an extension of the rodlike terminal, and the damper body carries a coupler section having the tapered hole. The change in cynamic system energy-that difference between the dynamic energy of the rodlike terminal just before coupling and the dynamic energy of the damper body rodlike terminal combination after coupling-is absorbed primarily by deformation (enlargement) of the taper hole and to a lesser extent by deformation (elongation) of the taper pin. This coupling is self-locking under conditions of either light or heavy coupling and provides a nonbounce coupling. Depth of engagement of the taper pin into the hole is roughly a direct function of the square root of rodlike terminal energy before coupling or with fixed rodlike terminal and damper body masses, a direct function of rodlike terminal velocity before coupling.

The damper body is held stationary by a pin or pawl extending into a receiving hole in the fuse housing. The damper body must be held securely enough to withstand all possible shipping and handling shocks that the fuse unit might encounter up to an amount that would damage other vital parts of the fuse structure. This was determined to be times the acceleration of gravity as a shock loading in any direction 100 g.). In the case of a 3-pound damper body, this withstand figure, longitudinally is 300 pounds. The damper body latching mechanism is released by the rodlike terminal. The energy necessary to unlatch is only a very small portion of the energy available. These available energies, just prior to damper body engagement, vary between 50 inch-pounds for no-load operation and 1,500 inch-pounds for maximum fault.

Among the objects of this invention are: To provide for reducing the speed of a rodlike terminal in an alternating-current high-voltage power fuse after it has been moved a predetermined distance on blowing of a fusible element; to couple the rodlike terminal to a damper body for accelerating the latter and reducing the speed of the former; effect the coupling in a nonbounce fashion; to dissipate some of the kinetic energy of the rodlike terminal in making the nonbounce coupling; to latch the damper body stationary in a fuse housing such that it does not move in'response to normal shock loading to which the fuse may be subjected; and to unlatch the damper body for movement conjointly with the rodlike terminal when the latter moves into coupling relation to the former.

In the drawings:

FIG. 1 is a view, in side elevation, of a typical mounting arrangement for hinge and latch assemblies for the dropout fuse disclosed herein.

FIG. 2 is a view, in side elevation, of a dropout fuse provided with trunnion and fuse tube release assemblies arranged for cooperating with the hinge and latch assemblies of the mounting shown in FIG. 1.

FIGS. 3a, 3b, 3c and 3d positioned one above the other with FIG. 3a at the bottom show a vertical longitudinal cross-sectional sectional view of the fuse shown in FIG. 2, the showing here at an enlarged scale.

FIG. 4 is perspective view of the cross slide latch that is employed for holding the damper body against movement.

FIG. 5 is a view similar to portions of FIGS. 3b and 3c and shows the rodlike terminal having been released and the damper body unlatched but not coupled.

FIG. 6 is a view similar to FIG. 5 showing the damper body unlatched and coupled for conjoint movement to the rodlike terminal.

FIG. 7 is a view at an enlarged scale, partly in side elevation and partly in section, of the upper end of the dropout fuse, the showing being in the unlatched position of the latch release tube prior to permitting the fuse to swing to the open or dropped out position.

FIG 8 is a view, similar to FIGS. 3b and 3c, showing a modified latch.

FIG. 9 is a view, in side elevation, of FIG. 8.

FIG. 10 is a view, similar to FIG. 8, showing how the latch is unlatched.

In FIG. 1 reference character 10 designates, generally, a mounting for a alternating current circuit interrupter of the fuse type and particularly of the dropout fuse type. However, it will be understood that the present invention can be employed in a fuse of the nondropout type. The mounting 10 includes a channel base 11 which is provided with lower and upper insulators 12 and 13 near its ends. The lower insulator 12 carries a hinge assembly that is indicated, generally, at 14 while the upper insulator 13 carries a latch assembly that is indicated, generally, at 15. In FIG. 2 there is indicated, generally, at 16 a dropout fuse which includes a fuse housing, indicated generally at 17, a trunnion assembly, indicated generally at 18, at its lower end and a latch release assembly, indicated generally at 19, at its upper end. The hinge assembly 14 is provided with trunnion receiving slots 22 which are arranged to receive trunnions 23 that extend from opposite sides of the trunnion assembly 18 for the purpose of pivotally mounting the dropout fuse 16. A bifurcated latch 24 is pivotally mounted at 25 on the latch assembly and it in cludes a roller 26 for latching engagement with a roller 27 that is carried by a hook 28 which extends laterally from a metallic fitting 29 which forms a part of the fuse housing 17 and is located near its upper end. The roller 27 is arranged to underlie the roller 26 for the purpose of holding the dropout fuse 16 in the operative upright position. Nose portions 30 are provided on the forward end of the bifurcated latch 24 for engaging the upper side ofa radial flange 31 which is located at the lower end of a latch release tube 32. When the latch release tube 32 is moved upwardly, for example, by a pivoted pull ring 33, the latch 24 is lifted to disengage the roller 26 from the roller 27 and permit the fuse 16 to swing about the trunnions 23 to the open circuit position.

In FIG. 3a it will be observed that a lower terminal or ferrule 37 is located at the lower end of the fuse housing 17. It is connected to the hinge assembly 14 through the trunnion assembly 18 to provide a circuit therebetween. The terminal of ferrule 37 is connected by an inner metallic ring 38 and sleeve 38' to a metallic bridge 39 which extends across the lower discharge end of the fuse housing 17. A terminal rod 40 extends through the metallic bridge 39 and is secured in position thereon by nuts 41. The terminal rod 40 constitutes a stationary arcing terminal. The lower end of the fuse housing 17 is closed by a closure disc 42 which is blown out on operation of the fuse. A fusible element 43 is connected to the upper end of the terminal rod 40. The fusible element 43 includes a fuse wire 44 and a strain wire 45 the upper ends of which are connected to the lower end of a rodlike terminal 46. The rodlike terminal 46 is movable upwardly through a bore 47 that is formed in cakes 48 of a suitable arc extinguishing material, such as boric acid. It will be understood, that, when the fusible element 43 blows on flow therethrough of current in excess of a predetermined current, the rodlike terminal 46 moves upwardly through the bore 47 from the surface of which an arc extinguishing medium is evolved. Incident to the drawing of the arc and upward movement of the rodlike terminal 46 is the application thereto of gas pressure which acts to drive the rodlike terminal 46 upwardly in addition to the force exerted thereon by a spring to be described.

FIG. 3b shows the details of construction of the fuse 16 immediately above those illustrated in FIG. 3a. Here it will be observed that the rodlike terminal 46 extends upwardly through additional cakes 48 of arc extinguishing material and that it is provided with an enlarged contact section 51 having contact fingers 52 in engagement therewith. The contact fingers 52 extend upwardly from a contact fitting 53 which is secured to a contact sleeve 54 that is located at the lower end of and is connected to an upwardly extending tubular contact terminal 55. As shown in FIG. 3c the upper end of the tubular contact terminal 55 is connected to a contact fitting 56 which forms a part of the fuse housing [7 and is connected directly to the metallic fitting 29 to complete a circuit therethrough to the latch-assembly 15. A coil compression spring 57, FIG. 3b, is interposed between the upper side of the contact sleeve 54 and the under side of a rod end fitting 58 which is secured to the upper end of the rodlike terminal 46. In this manner the rodlike terminal 46 is biased upwardly for movement through the bore 47, the spring force being restrained by the fusible element 43 as long as it remains intact.

As pointed out hereinbefore it is desirable to limit the speed of the rodlike terminal 46 after blowing of the fusible element 43 and on movement of the rodlike terminal 46 to a predetermined position under the combined influences of the gas pressure, previously referred to, and the force exerted by the coil compression spring 57. In accordance with this invention a guide tube 61 is secured to the metallic fitting 29 and extends upwardly therefrom for receiving therein a metallic damper body 62. When released, the metallic damper body 62 is freely slidable upwardly through the. guide tube 61. Under normal operating conditions before the fusible element 43 is blown it is desirable that the damper body 62 be held against any movement. The reason for this is to avoid any displacement of it when the fuse 16 is subjected to shocks incident to shipping, handling, etc. For this purpose the damper body 62 is provided with a transverse slot 63 in which a metallic cross-slide latch 64 is located. This latch is shown in detail in FIG. 4. It has a latch pin extension 65 which is arranged to extend into a latch opening 66 that is located, in part, in the upper end of the contact terminal 55 and in part in the contact fitting 56. It will be understood that the latch opening 66 is located in the fuse housing 17 for receiving the latch pin extension 65 to prevent endwise movement of the damper body 62. A leaf spring 67 is employed for biasing the cross-slide latch 64 to the latched position. The leaf spring 67 is secured at 68 to the damper body 62. Its distal end 69 bears against one end of the cross-slide latch 64 to hold it in the latched position shown in FIG. 3c. The cross-slide latch 64 is provided with a central circular opening 70 having a tapered entrance opening 71.

It is necessary to unlatch the damper body 62 when the rodlike terminal 46 has moved upwardly through a predeter-v mined extent so that subsequently the two can be coupled together for continued conjoint movement at a reduced speed. For this purpose a tapered section 72 of a metallic ram pin 73 is arranged to enter the entrance opening 71 and to move into the opening 70 in the cross-slide latch 64 as illustrated in FIG. 5. This action shifts the cross-slide latch 64 from the latched position and withdraws the latch pin extension 65 from the latch opening 66. The damper body 62 then is free to move upwardly through the guide tube 61 conjointly with the rodlike terminal 46. The ram pin 73 has a cylindrical section a 74 for fully entering the cylindrical opening 70 in the crossslide latch 64 and holding it in the unlatched position. The damper body 62 has a central opening 75 opposite a button head 76 on the ram pin 73 against which a coil compression spring 77 in the opening 75 reacts to bias the ram pin 73 downwardly to the latching position against a shoulder 78 provided by a coupler ring 81 to be described.

It is important that the rodlike terminal 46 be securely coupled to the damper body 62 and that there be no bounce to the coupling. For this purpose coupling means is employed and is secured to the lower end of the damper body 62 by screws one of which is indicated at 80 in FIG. 3c. The screws 80 extend through a metallic coupler ring 81 which has a central opening 82 and a tapered entrance opening 83. A reduced diameter impact end 84 of the ram pin 73 extends downwardly through the central opening 82 and projects therebelow. The lower end of the impact end 84 of the ram pin 73 is arranged to be engaged by an upper end 85, FIG. 3b, of a metallic coupling tip 86 which actually is an extension of the rodlike terminal 46. At its lower end the coupling tip 86 has an extension 87 that is threaded at 88 into the upper end of the rod end fitting 58. It will be understood that the metallic coupling tip 86 constitutes a unitary construction with the rodlike terminal 46. The coupling tip 86 has a beveled upper end 89 and a tapered section 90 for entering the central opening 82 and tapered entrance opening 83 in the metallic coupler ring 81.

FIG. 5 shows the position of the rodlike terminal 46 and parts movable therewith just after the metallic ram pin 73 has been engaged and moved upwardly sufficiently far to unlatch the cross-slide latch 64 by moving the latch pin extension 65 out of the latch opening 66. Here the beveled end 89 of the metallic coupling tip 86 is shown as extending through the central opening 82 in the metallic coupler ring 81. As yet the damper body 62 has not been moved upwardly.

FIG. 6 shows the subsequent relationship between the rodlike terminal 46 and the damper body 62 when they are moving upward conjointly under the combined influences of the coil compression spring 57 and the gas pressure that is applied to the rodlike terminal 46. Here it will be observed that he tapered section 90 has been driven into the central opening 82 in the metallic coupler ring 81. A substantial part of the kinetic energy of the moving rodlike terminal 86 is dissipated in the deformation of the metallic coupler ring 81 and in the elongation of the tapered section 90. This absorption of kinetic energy is in addition to the kinetic energy that is dissipated in accelerating the damper body 62 in moving upwardly. There is a corresponding reduction in the speed of upward movement of the rodlike terminal 46 and a corresponding reduction in the length of the gap between the upper end of the terminal rod 40, FIG. 3a, and the retreating lower end of lower rodlike terminal 46. The advantages flowing from this relationship have been outlined hereinbefore.

The rodlike terminal 46 and the damper body 62 continue their upward movement until finally the upper end of the damper body 62 engages the underside of a-closure cap 94, FIGS. 3d and 7 which is located at the upper end of the latch release tube 32. The latch release tube 32 is moved upwardly to shift the radial flange 31 from the broken line position shown in FIG. 7 to the full line position there shown for lifting the latch 24 to the released position. The fuse 16 then swings downwardly about the trunnions 23 to the open circuit position.

In FIG. 3c it will be observed that the latch release tube 32 is telescoped over the guide tube 61 which directs the upward movement of the damper body 62. The latch release tube 32 is biased downwardly by a coil compression spring which reacts between the underside of a washer 96 that bears against a shoulder 97 on theguide tube 61 and the upper end of a tubular upwardly extending extension of the radial flange 31 which is secured to the lower end of the latch release tube 32. That extension is indicated at 98. The downward movement of the latch release tube 32 is limited by a rain shield 99. A sleeve overlies the lower portion of the extension 98 and the upper portion of the rain shield 99 to limit the entrance of moisture therebetween.

In FIGS. 8, 9 and 10 there is illustrated an alternate form of latch release mechanism. Here it will be observed that the same fuse housing 17 is employed together with the parts associated with the rodlike terminal 46 previously described as well as the damper body 62. The latch mechanism here disclosed includes a latch level which is pivoted at 106 intermediate its ends on a metallic frame that is indicated, generally, at 107. The metallic frame 107 is located in a lon gitudinal slot 108 that is formed in the damper body 62 to one side thereof. A screw 109 holds the metallic frame 107 in position on the damper body 62. The latch lever 105 includes at its upper end a latch pin 110 which is integral therewith and which is arranged to move through an opening 111 in the frame 107 and into latching engagement with the latch opening 66 which extends through the contact terminal 55 and the contact fitting 56 or into the fuse housing 17. A leafspring 112 is secured at one end at 113 to the metallic frame 107. Its distal end reacts against the upper end of the latch lever 105 to bias the latch pin 110 to the latching position. The lower end 114 of the latch level 105 is engaged by a trigger lever 115 which is pivoted at 116 in the slot 108. In operation when the rodlike terminal 46 moves upwardly as previously described the metallic coupling tip 86 moves through the central opening 82 in the metallic coupler ring 81 to the position shown in FIG. 10. The beveled end 89 engages the trigger lever 115 and pivots it in a clockwise direction to, in turn, pivot the latch 105 in a counter clockwise direction to withdraw the latch pin 110 from the latch opening 66 and to move it against a stop pin 117 which extends across the slot 108 in the damper body 62.

As before deformation of the metallic coupler ring 81 and elongation of the tapered section 90 of the coupling tip 86 absorbs some of the kinetic energy of the moving rodlike terminal 46. Additional energy is absorbed in accelerating the damper body 62.

In both latching embodiments of the invention there is nonbounce engagement between the metallic coupling tip 86 and the metallic coupler ring 81. This is due to the tapered relationship of the engaging surfaces and the forces with which they are drive together.

In fuse devices of the type disclosed in the above Barta patent acceleration of the rodlike terminal is uncontrolled, It is a function of spring energy and gas pressure and, as indicated, may result in excessive lengthening of the arc. According to this invention in that portion of the stroke of the rodlike terminal 46 during which the arc is drawn or at 20 to 30 percent of the total stroke, the floating damper body 62 is engaged with the result that there is a corresponding reduction in acceleration and a corresponding reduction in the lengthening of the are for the purposes above outlined. This is in contradistinction to the construction disclosed in Triplett U.S. Pat. No. 2,087,744, issued July 20, 1937 in which, like the Barta patent, the acceleration of the rodlike terminal is uncontrolled throughout the initial portion of its stroke during which the arc is drawn and extinguished. Beginning at about 42 to 62 percent of the total stroke, the acceleration of the rodlike terminal of the Triplett patent is reduced until about 77 to 83 percent of the total stroke to permit engagement of a circuit reclosing contact without bouncing and to provide a time delay in the completion of a circuit to another fuse to reestablish the energization of a load circuit.

An important advantage of the control of the arc length by decelerating the rodlike terminal 46 beginning at to percent of its total stroke is the extinguishment of the are before the upper end of the damper body 62 engages the underside of the closure cap 94 to unlatch the latch 24 to permit the fuse 16 to swing from the upright position to the depending open circuit position. Since the arc is always extinguished before the fuse 16 is unlatched, there is no likelihood that an arc will be drawn in air between a stationary contact 118 on the upper insulator l3 and the metallic fitting or contact 29 of the upper end of the fuse housing 17.

The latch mechanism comprising the cross-slide 64 and the ram pin 73 is disclosed and claimed in copending Scherer application, Ser. No. 104,552, filed Jan. 7, 197] and assigned to the assignee of this application.

What is claimed as new is:

1. An altemating-current circuit interrupter comprising: a housing, a body of arc extinguishing material in said housing having a bore from which an arc extinguishing gas is evolved due to the heat of an arc, a stationary terminal on said housing at one end of said bore, a rodlike terminal movable in said bore, spring means in said housing biasing said rodlike terminal for movement through said bore, fusible means interconnecting said terminals and adapted to blow or flow therethrough of predetermined alternating current whereupon an arc is drawn between said terminals and said rodlike terminal is moved through said bore by pressure of gas evolved from said bore and by said spring and is extinguished after one or more current zeros, and means reacting against said rodlike terminal during the period in which said arc is drawn for reducing the speed at which said rodlike terminal is moved by said spring means to effect a corresponding reduction in the speed at which said are is lengthened.

2. The circuit interrupter according to claim 1 wherein said means reacting against said rodlike terminal comprises a damper body that is engaged by said rodlike terminal after it has moved a predetermined distance from its initial position.

3. The circuit interrupter according to claim 2 wherein latch means hold said damper body against movement until unlatched as a result of movement of said rodlike terminal through said predetermined distance.

4. The circuit interrupter according to claim 2 wherein coupler means operative on engagement of said damper body by said rodlike terminal absorb by deformation a portion of the kinetic energy of the moving rodlike terminal and maintain said rodlike terminal and said damper body inseparable for the remainder of the stroke of the former.

5. The circuit interrupter according to claim 1 wherein said circuit interrupter is a dropout type fuse latched in circuit closed position, and said arc is drawn and extinguished before said fuse is unlatched from circuit closed position.

6. An alternating-current circuit interrupter comprising: a housing, a body of arc extinguishing material in said housing having a bore from which an arc extinguishing gas is evolved due to the heat of an arc, a stationary terminal on said housing at one end of said bore, a rodlike terminal movable in said bore, spring means in said housing biasing said rodlike terminal for movement through said bore, fusible means interconnecting said terminals and adapted to blow on flow therethrough of predetermined alternating current whereupon an arc is drawn between said terminals and said rodlike terminal is moved through said bore by pressure gas evolved from said bore and by said spring and is extinguished after one or more current zeros, and a damper body movable endwise of said bore in said housing and arranged to be engaged by said rodlike terminal after it has been moved a predetermined distance on blowing or said fusible means during the period in which said arc is drawn to effect conjoint movement of said rodlike terminal and said damper body and corresponding reduction in the speed of said rodlike terminal with a consequent decrease in its movement during successive half cycles of alternating current arcing.

7. The circuit interrupter according to claim 6 wherein latch means hold said damper body against movement, and means on said rodlike terminal unlatch said latch means on movement of said rodlike terminal through said predetermined distance.

8. The circuit interrupter according to claim 6 wherein coupler means operative on engagement of said damper body'by said rodlike terminal absorb by deformation a portion of the kinetic energy of the moving rodlike terminal and maintain said rodlike terminal and said damper body inseparable for the remainder of the stroke of the former.

9. The circuit interrupter according to claim 6 wherein said circuit interrupter is a dropout type fuse latched in circuit closed position, and said arc is drawn and extinguished before said fuse is unlatched from circuit closed position.

10. An altemating-current circuit interrupter comprising: a housing, a body of arc extinguishing material in said housing having a bore from which an arc extinguishing gas is evolved due to the heat of an arc, a stationary terminal on said housing at one end of said bore, a rodlike terminal movable in said bore, spring means in said housing biasing said rodlike terminal for movement through said bore, fusible means interconnecting said terminals and adapted to blow on flow therethrough of predetermined alternating current whereupon an arc is drawn between said terminals and said rodlike terminal is moved through said bore by pressure of gas evolved from said bore and by said spring and is extinguished after one or more current zeros, a damper body movable endwise of said bore in said housing and arranged to be engaging by said rodlike terminal after it has been moved a predetermined distance on blowing of said fusible means, latch means for holding said damper body against movement in said housing, and means for releasing said latch means on movement of said rodlike terminal through said predetermined distance to effect conjoint movement of said rodlike terminal and said damper body and corresponding reduction in the speed of said rodlike terminal with a consequent decrease in its movement during successive half cycles of the alternating current.

11. The circuit interrupter according to claim 10 wherein said latch releasing means includes: latch pin means mounted for transverse movement on said damper body and normally in latching engagement with said housing, and means movable with said rodlike terminal for displacing said latch pin means and freeing said damper body for said conjoint movement.

12. The circuit interrupter according to claim 11 wherein said latch pin means includes a latch lever pivoted intermediate its ends on said damper body and having a laterally extending latch pin at one end for entering a latch opening in said housing, and means extend from said rodlike terminal for displacing the other end of said lever to withdraw said latch pin from said opening in said housing.

13. The circuit interrupter according to claim 10 wherein said damper body includes metallic coupler means having a tapered opening therein, and said rodlike terminal has a metallic tapered coupling tip extending endwise therefrom for entering said opening in said coupler means whereby the engaging portions thereof are deformed and part of the kinetic energy of the moving rodlike terminal is dissipated by causing such deformation.

14. The circuit interrupter according to claim 13 wherein said latch releasing means includes latch pin means mounted for transverse movement on said damper body and normally in latching engagement with said housing, and said coupling tip is arranged to displace said latch pin means and free said damper body for conjoint movement with said rodlike terminal.

15. The circuit interrupter according to claim 13 wherein said latch pin means includes a latch level pivoted intermediate its ends on said damper body and having a laterally extending latch pin at one end for entering a latch opening in said housing, and said coupling tip is arranged to displace the other end of said lever to withdraw said latch pin from said opening in said housing. 

1. An alternating-current circuit interrupter comprising: a housing, a body of arc extinguishing material in said housing having a bore from which an arc extinguishing gas is evolved due to the heat of an arc, a stationary terminal on said housing at one end of said bore, a rodlike terminal movable in said bore, spring means in said housing biasing said rodlike terminal for movement through said bore, fusible means interconnecting said terminals and adapted to blow or flow therethrough of predetermined alternating current whereupon an arc is drawn between said terminals and said rodlike terminal is moved through said bore by pressure of gas evolved from said bore and by said spring and is extinguished after one or more current zeros, and means reacting against said rodlike terminal during the period in which said arc is drawn for reducing the speed at which said rodlike terminal is moved by said spring means to effect a corresponding reduction in the speed at which said arc is lengthened.
 2. The circuit interrupter according to claim 1 wherein said means reacting against said rodlike terminal comprises a damper body that is engaged by said rodlike terminal after it has moved a predetermined distance from its initial position.
 3. The circuit interrupter according to claim 2 wherein latch means hold said damper body against movement until unlatched as a result of movement of said rodlike terminal through said predetermined distance.
 4. The circuit interrupter according to claim 2 wherein coupler means operative on engagement of said damper body by said rodlike terminal absorb by deformation a portion of the kinetic energy of the moving rodlike terminal and maintain said rodlike terminal and said damper body inseparable for the remainder of the stroke of the former.
 5. The circuit interrupter according to claim 1 wherein said circuit interrupter is a dropout type fuse latched in circuit closed position, and said arc is drawn and extinguished before said fuse is unlatched from circuit closed position.
 6. An alternating-current circuit interrupter comprising: a housing, a body of arc extinguishing material in said housing having a bore from which an arc extinguishing gas is evolved due to the heat of an arc, a stationary terminal on said housing at one end of said bore, a rodlike terminal movable in said bore, spring means in said housing biasing said rodlike terminal for movement through said bore, fusible means interconnecting said terminals and adapted to blow on flow therethrough of predetermined alternating current whereupon an arc is drawn between said terminals and said rodlike terminal is moved through said bore by pressure gas evolved from said bore and by said spring and is extinguished after one or more current zeros, and a damper body movable endwise of said bore in said housing and arranged to be engaged by said rodlike terminal after it has been moved a predetermined distance on blowing or said fusible means during the period in which said arc is drawn to effect conjoint movement of said rodlike terminal and said damper body and corresponding reduction in the speed of said rodlike terminal with a consequent decrease in its movement during successive half cycles of alternating current arcing.
 7. The circuit interrupter according to claim 6 wherein latch means hold said damper body against movement, and means on said rodlike terminal unlatch said latch means on movement of said rodlike terminal through said predetermined distance.
 8. The circuit interrupter according to claim 6 wherein coupler means operative on engagement of said damper body by said rodlike terminal absorb by deformation a portion of the kinetic energy of the moving rodlike terminal and maintain said rodlike terminal and said damper body inseparable for the remainder of the stroke of the former.
 9. The circuit interrupter according to claim 6 wherein said circuit interrupter is a dropout type fuse latched in circuit closed position, and said arc is drawn and extinguished before said fuse is unlatched from circuit closed position.
 10. An alternating-current circuit interrupter comprising: a housing, a body of arc extinguishing material in said housing having a bore from which an arc extinguishing gas is evolved due to the heat of an arc, a stationary terminal on said housing at one end of said bore, a rodlike terminal movable in said bore, spring means in said housing biasing said rodlike terminal for movement through said bore, fusible means interconnecting said terminals and adapted to blow on flow therethrough of predetermined alternating current whereupon an arc is drawn between said terminals and said rodlike terminal is moved through said bore by pressure of gas evolved from said bore and by said spring and is extinguished after one or more current zeros, a damper body movable endwise of said bore in said housing and arranged to be engaging by said rodlike terminal after it has been moved a predetermined distance on blowing of said fusible means, latch means for holding said damper body against movement in said housing, and means for releasing said latch means on movement of said rodlike terminal through said predetermined distance to effect conjoint movement of said rodlike terminal and said damper body and corresponding reduction in the speed of said rodlike terminal with a consequent decrease in its movement during successive half cycles of the alternating current.
 11. The circuit interrupter according to claim 10 wherein said latch releasing means includes: latch pin means mounted for transverse movement on said damper body and normally in latching engagement with said housing, and means movable with said rodlike terminal for displacing said latch pin means and freeing said damper body for said conjoint movement.
 12. The circuit interrupter according to claim 11 wherein said latch pin means includes a latch lever pivoted intermediate its ends on said damper body and having a laterally extending latch pin at one end for entering a latch opening in said housing, and means extend from said rodlike terminal for displacing the other end of said lever to withdraw said latch pin from said opening in said housing.
 13. The circuit interrupter according to claim 10 wherein said damper body includes metallic coupler means having a tapered opening therein, and said rodlike terminal has a metallic tapered coupling tip extending endwise therefrom for entering said opening in said coupler means whereby the engaging portions thereof are deformed and part of the kinetic energy of the moving rodlike terminal is dissipated by causing such deformation.
 14. The circuit interrupter according to claim 13 wherein said latch releasing means includes latch pin means mounted for transverse movement on said damper body and normally in latching engagement with said housing, and said coupling tip is arranged to displace said latch pin means and free said damper body for conjoint movement with said rodlike terminal.
 15. The circuit interrupter according to claim 13 wherein said latch pin means includes a latch level pivoted intermediate its ends on said damper body and having a laterally extending latch pin at one end for entering a latch opening in said housing, and said coupling tip is arranged to displace the other end of said lever to withdraw said latch pin from said opening in said housing. 